Articles which have been produced by means of additive manufacturing methods (“3D printing”) can have uneven surfaces because of the manner in which they have been produced. With regard to thermoplastic construction materials, this applies to articles produced both by powder-based methods, which have unevenness determined by the particle size in the powder and the layer thickness of each newly applied powder layer, and by melt coating methods, which have unevenness determined by the thickness of the strand applied. However, such unevenness is undesirable from the point of view of tactile and optical properties of the article and because of the fact that uneven surfaces are more easily soiled.
There has been no lack of attempts in the prior art to improve the outward appearance or technical function of 3D-printed articles by an aftertreatment of their surface. A material-removing, mechanical aftertreatment (including sandblasting) is undesirable in many cases. The articles can also be treated with solvent vapours which partly dissolve the surfaces and, after evaporation of the solvent, a smoothed surface is obtained. However, the use of organic solvents is fundamentally problematic.
WO 2011/089208 A1 discloses a process for surface treatment of laser-sintered plastics articles, wherein the following steps are executed: a) smoothing the surfaces of plastics articles; b) washing the smoothed plastics articles; c) coloring and/or coating the plastics articles and d) sealing and/or impregnating the surfaces of the plastics articles.
DE 10 2015 205609 A1 takes another route by applying an additional layer to the surface of the article. It is a feature of the process described therein for powder bed-based additive manufacturing of a component, in which the component is produced layer by layer in a powder bed of powder particles by melting with a beam of energy, that, on conclusion of the production of one layer of the component, a film filled with added particles is applied to the component, wherein the added particles differ from the powder particles in terms of their properties and the film material of the film is removed with the beam of energy, wherein the application of energy by the beam of energy is sufficient to cause permanent bonding of the added particles to the component.